This invention relates to an antioxidant composition of a mixture of para-butylated and octylated, ortho-ethylated diphenylamines, which composition is a liquid at ambient conditions and is particularly useful as an antioxidant for petroleum based and synthetic lubricants.
The role of an antioxidant is to prevent or inhibit the oxidation of organic materials such as petroleum based lubrications. Alkylated diphenylamines are known as useful antioxidants.
Some examples of alkylated diphenylamine antioxidants include 4,4'-bis PA0 (.alpha.,.alpha.-dimethylbenzyl)diphenylamine and other compounds described in U.S. Pat. No. 3,649,690; PA0 2,2'-diethyl-4,4'-di-t-octyldiphenylamine and other compounds described in U.S. Pat. No. 3,732,167; PA0 2,2',4,4'-tetra-t-butyldiphenylamine and other compounds described in U.S. Pat. No. 3,655,559; and PA0 p,p'-di-t-octyldiphenylamine and p,p'-di(.alpha.-phenylethyl)diphenylamine described in U.S. Pat. No. 2,530,769. PA0 2,2'-diethyldiphenylamine; PA0 4,4'-di-t-octyl-2,2'-diethyldiphenylamine; PA0 4-t-octyl-2,2'-diethyldiphenylamine; PA0 4-t-butyl-2,2'-diethyldiphenylamine; PA0 4,4'-di-t-butyl-2,2'-diethyldiphenylamine; and PA0 4-t-butyl-4-t-octyl-2,2'-diethyldiphenylamine.
Para- and ortho-alkylated diphenylamines are typically prepared using a two-stage process such as the one described in the U.S. Pat. No. 3,655,559 patent referenced above. In the first stage, diphenylamine (DPA) is alkylated at one or both of the ortho-(2,2') positions by alkylating diphenylamine with a first olefin. The intermediate compound is then washed or isolated, and, in the second stage, the compound is para-alkylated using a second olefin.
Another process for preparing para-, ortho-alkylated diphenylamines involves a one-stage process where the ortho-alkylated intermediate product is not isolated from the reaction mix but is para-alkylated in the reaction mix to provide the final product. This one-stage process is fully described in a copending application for patent filed on Aug. 29, 1986 and entitled "Improved Process For the Preparation of Ortho-, Para-Alkylated Diphenylamines". The disclosure of this copending application is hereby incorporated by reference.
A problem with using known alkylated diphenylamines as antioxidants, particularly for lubricating fluids, is that the compounds are typically solids and not readily dispersable or soluble in the polymer or fluids. For example, a well-known para-alkylated diphenylamine, which is used as an antioxidant, is 4,4'-di-(.alpha.,.alpha.-diphenylethyl) diphenylamine (Naugard 445). This compound is a solid at ambient temperatures.
Another well-known para-, ortho-alkylated diphenylamine, which is used as an antioxidant, is 2,2'-diethyl-4,4'-di-t-octyldiphenylamine (OEPA), which is described both in the 3,655,559 and 3,732,167 patents previously referenced. The pure compound, OEPA, crystallizes at about 63.degree. C. (145.4.degree. F.).
An example of a para-alkylated diphenylamine which is liquid at ambient temperatures is the composition mixture described in European Patent Office application No. 0,149,422 to Ciba-Giegy AG. This composition is a specific mixture of para-octylated and para-butylated diphenylamines, wherein the 4,4'-di-t-octyldiphenylamine in the mixture must be below 30% by weight total in the mix. An example of a para-, ortho-alkylated diphenylamine which is liquid at ambient temperature is 4,4'-dinonyl-2,2'-diethyl diphenylamine (Agerite NEPA).
It is an object of the present invention to provide a novel composition comprising a mixture of para-octylated and butylated, ortho-ethylated diphenylamines, which composition is liquid at ambient temperatures, and, as such, is particularly useful as an antioxidant for petroleum based and synthetic lubricants.